Fuel supply system for a natural gas-powered internal combustion engine

Abstract

Fuel supply system for a natural gas-powered internal combustion engine, comprising a fuel tank (1) for storing liquefied natural gas and an electrically driven fuel pump (2) for pumping the liquefied natural gas at high pressure, wherein the fuel pump (2) is designed as a radial piston pump, which has at least one pump element (3) with a pump piston (4) which defines a pump working chamber (5) and can be driven in a stroke motion via a shaft (7) connected to an electric motor (6) and the fuel pump (2) is driven via the electric motor (6).

Description

[0001] The invention relates to a fuel supply system for an internal combustion engine that can be operated with natural gas, comprising a fuel tank for storing liquefied natural gas and an electrically driven fuel pump for conveying the liquefied natural gas at high pressure. State of the art

[0002] German patent application DE 10 2011 088 795 A1 discloses a fuel system for an internal combustion engine that can be operated with at least two types of fuel and includes an electrically driven high-pressure fuel pump for at least one of the two fuel types. The high-pressure fuel pump is connected at its output to a high-pressure line common to both fuel types, through which an injection device can be supplied with compressed fuel of either type. The first fuel can be, in particular, gasoline or diesel fuel, while liquefied petroleum gas (LPG) or another fuel with a comparatively high vapor pressure is proposed as the second fuel. The second fuel is thus a gas, such as autogas (LPG).“Liquefied Petroleum Gas”), which remains liquid under pressure even at normal temperatures, making it possible to use a common high-pressure line for both types of fuel.

[0003] Document US 2005 / 0086949A1 discloses a cryogenic tank arrangement comprising a container with a cryogenic chamber capable of storing a cryogenic fluid at an initial pressure. The arrangement further includes a pump with an inlet port capable of receiving a quantity of the cryogenic fluid, pressurizing it to a pressure above its storage pressure, and delivering it to an accumulator within the cryogenic chamber.

[0004] Document JP 2006 - 29 157 A shows a liquid gas fuel supply device in which a fuel pump is divided into a separable drive part and a pump part.

[0005] Document DE 11 2016 002 683 T5 discloses a cryofluid pump with multiple pumping elements, each pumping element comprising an actuator section, an activation section, and a pumping section. The actuator section is connected to one end of a push rod and is configured to be selectively activated in response to a command from an electronic control unit, thereby activating the activation section to pump a fluid.

[0006] Natural gas (NG) is gaseous at normal temperatures, even under high pressure (compressed natural gas, CNG). Therefore, special injection valves are required to inject compressed natural gas into the combustion chamber of an internal combustion engine; these differ from those used for the direct injection of gasoline or diesel fuel. Since liquefied natural gas (LNG) has a significantly smaller volume than gaseous natural gas, it is generally stored in liquid form for mobile applications. For this purpose, the natural gas is cooled to temperatures of approximately -160 °C.

[0007] Therefore, operating an internal combustion engine with natural gas requires a fuel supply system specifically adapted to this type of fuel.

[0008] The invention is based on the objective of providing such a fuel supply system for an internal combustion engine that can be operated with natural gas and that is also simple in design and cost-effective to implement.

[0009] To solve the problem, the fuel supply system with the features of claim 1 is specified. Advantageous embodiments of the invention can be found in the dependent claims. Disclosure of the invention

[0010] The proposed fuel supply system for a natural gas-powered internal combustion engine comprises a fuel tank for storing liquefied natural gas and an electrically driven fuel pump for delivering the liquefied natural gas at high pressure. The fuel pump is a radial piston pump and has at least one pump element with a piston that defines a pump working chamber and is driven in a reciprocating motion via a shaft connected to an electric motor.

[0011] The proposed fuel supply system therefore uses a fuel pump similar in design to that of a diesel fuel injection system. This allows existing components of such a radial piston pump to be used, simplifying the design and reducing costs. However, unlike conventional radial piston pumps, the fuel pump in the proposed system is driven by an electric motor, which offers further advantages.

[0012] According to a preferred embodiment of the invention, the delivery rate of the fuel pump in the proposed fuel supply system can be controlled via the speed of the electric motor. The fuel pump can therefore be arranged spatially remote from the internal combustion engine, thus protecting it from the engine's temperature influence.

[0013] Preferably, the electric motor is / are arranged outside the fuel tank and / or the fuel pump is arranged wholly or partially inside the fuel tank. This means that the shaft connected to the electric motor for driving the fuel pump is preferably made comparatively long. Arranging the electric motor outside the fuel tank has the advantage that hardly any waste heat from the electric motor is transferred into the fuel stored in the fuel tank.

[0014] Furthermore, the fuel pump preferably has an engine chamber that can be filled with liquefied natural gas, through which the pump working chamber of the pump element can be supplied with liquefied natural gas. The fuel stored in the fuel tank is thus fed to the pump working chamber of the pump element via the engine chamber. This prevents heat from being transferred from the fuel pump to the tank via the fuel, since the components of the fuel pump that generate heat loss are primarily located in the engine chamber, such as the engine itself, which can be designed, for example, as a cam or eccentric drive, and the shaft bearings. The engine chamber is also preferably formed in a pump housing, in which, at least partially, the shaft connected to the electric motor is also accommodated.

[0015] Furthermore, it is proposed that the pump element have an inlet valve on the suction side, through which the pump working chamber can be connected to the engine chamber. The inlet valve can, for example, be designed as a simple check valve that prevents backflow of fuel against the direction of delivery, so that pressure can be built up in the pump working chamber during operation of the fuel pump.

[0016] On the pressure side, the pump element preferably has an outlet valve through which the pump working chamber can be connected to a high-pressure line. The outlet valve can also be designed as a simple check valve that opens when the pressure in the pump working chamber exceeds a predetermined opening pressure of the outlet valve. Preferably, the high-pressure line connected to the outlet valve can be connected to the engine compartment via a pressure relief valve. The pressure relief valve prevents the pressure in the high-pressure line from rising above a predetermined limit, as it opens beforehand and returns a portion of the fuel previously delivered at high pressure back to the engine compartment.

[0017] Furthermore, the fuel supply system according to the invention preferably includes an evaporator arranged downstream of the fuel pump in the direction of natural gas flow. The evaporator is located outside the fuel tank and is connected to the pressure side of the fuel pump via the high-pressure line. Within the evaporator, the compressed natural gas is completely converted into a gaseous state.

[0018] In the direction of natural gas flow, downstream of the fuel pump and / or vaporizer, a high-pressure storage tank is preferably arranged. The compressed, now gaseous, natural gas is stored in the high-pressure storage tank and held in reserve for an injection device. The injection of the compressed gaseous natural gas into the combustion chamber of the internal combustion engine can be accomplished, for example, by means of an intake manifold. If the internal combustion engine is operated exclusively with natural gas (mono-fuel system), ignition is achieved using a spark plug. If the internal combustion engine can be operated with another fuel, such as diesel fuel (dual-fuel system), ignition can be effected by diesel injection. Furthermore, in a dual-fuel system, the natural gas can also be injected directly into the combustion chamber of the internal combustion engine. Direct injection necessarily requires the use of a high-pressure fuel pump, as this can only be achieved under high pressure.

[0019] Advantageously, the fuel pump of the proposed fuel supply system has at least two, preferably three, pump elements. This ensures a consistent delivery of natural gas at high pressure while maintaining low drive torque. Furthermore, the required storage volume of the high-pressure accumulator on the pressure side can be reduced. Preferably, all pump elements are supplied with liquefied natural gas via the engine compartment, resulting in a low pressure level within the engine compartment. This has the advantage of reducing the pressure load on the sealing elements in the area of ​​the shaft penetration to the electric motor, thus improving the seal.

[0020] The invention is explained in more detail below with reference to the accompanying drawing. This shows a schematic representation of a preferred embodiment of a fuel supply system according to the invention. Detailed description of the drawing

[0021] The schematically depicted fuel supply system comprises a fuel tank 1 for storing liquefied natural gas. A fuel pump 2, designed as a radial piston pump, is located inside the fuel tank 1. The fuel pump 2 has several pump elements 3 arranged radially around a shaft 7. For simplicity, only one pump element 3 is shown in the diagram. Each pump element 3 has a pump piston 4, the first end of which defines a pump working chamber 5 and the second end of which is supported by a cam 15 on the shaft 7. The shaft 7 is rotatably mounted via shaft bearings 16 and connected to an electric motor 6, which is located outside the fuel tank 1. The electric motor 6 drives the shaft 7 in a rotary motion. The cam 15 converts the rotary motion of the shaft 7 into a reciprocating motion of the pump pistons 4 supported thereon.The shaft 7 extends to the outside for connection with the electric motor 6, with a shaft seal 17 arranged in the area of ​​the bushing. The electric motor 6 has a tachometer 18, since the delivery rate of the fuel pump 2 can be controlled via the speed of the electric motor 6.

[0022] The shaft 7 is housed in a pump casing 19, which forms a pump chamber 8. The pump chamber 8 is filled with liquefied natural gas. The liquefied natural gas present in the pump chamber 8 is supplied to the pump working chambers of the pump elements 3 via an inlet valve 9. There, the liquefied natural gas is compressed and then discharged via an outlet valve 10 into a high-pressure line 11. If the pressure in the high-pressure line 11 rises above a permissible limit, a portion of the compressed natural gas is returned to the pump chamber 8 via a pressure relief valve 12.

[0023] The high-pressure line 11 connects the pressure side of the fuel pump 2 to a vaporizer 13. There, the compressed, still liquid natural gas is completely converted into a gaseous state. The gaseous natural gas is then fed to a high-pressure storage tank 14, which supplies an injection device (not shown) with the gaseous natural gas. A pressure and temperature sensor 20 is arranged on the high-pressure storage tank 14 to monitor the pressure and temperature. If the pressure exceeds a predetermined limit, pressure relief can be achieved via a pressure relief valve 21, which is also arranged on the high-pressure storage tank 14. Furthermore, a pressure regulating valve 22 and a shut-off valve 23 are arranged in the area of ​​the high-pressure storage tank 14.

[0024] A further pressure relief valve 24 is arranged on the fuel tank 1.

[0025] The depicted fuel supply system allows the use of components already known in a similar form from diesel fuel injection systems. This reduces costs. Furthermore, the depicted system is characterized by its simple design.

Claims

[1] Fuel supply system for a natural gas-powered internal combustion engine, comprising a fuel tank (1) for storing liquefied natural gas and an electrically driven fuel pump (2) for pumping the liquefied natural gas at high pressure, wherein the fuel pump (2) is designed as a radial piston pump, which has at least one pump element (3) with a pump piston (4) which defines a pump working chamber (5) and can be driven in a stroke motion via a shaft (7) connected to an electric motor (6) and the fuel pump (2) is driven via the electric motor (6). [2] Fuel supply system according to claim 1, characterized by , that the delivery rate of the fuel pump (2) can be controlled via the speed of the electric motor (6). [3] Fuel supply system according to claim 1 or 2, characterized by, that the electric motor (6) is located outside the fuel tank (1) and / or the fuel pump (2) is located wholly or partially inside the fuel tank (1). [4] Fuel supply system according to any one of the preceding claims, characterized by , that the fuel pump (2) has a motor chamber (8) that can be filled with liquid natural gas, through which the pump working chamber (5) of the pump element (3) can be supplied with liquid natural gas. [5] Fuel supply system according to claim 4, characterized by , that the pump element (3) has an inlet valve (9) on the suction side, via which the pump working chamber (5) can be connected to the engine chamber (8). [6] Fuel supply system according to one of claims 4 or 5 , characterized by, that the pump element (3) has an outlet valve (10) on the pressure side, via which the pump working chamber (5) can be connected to a high-pressure line (11), which is preferably connected to the engine room (8) via a pressure relief valve (12). [7] Fuel supply system according to any one of the preceding claims, characterized by , that an evaporator (13) is arranged downstream of the fuel pump (2) in the direction of delivery of the natural gas. [8] Fuel supply system according to any one of the preceding claims, characterized by , that a high-pressure storage tank (14) is arranged downstream of the fuel pump (2) and / or the evaporator (13) in the direction of delivery of the natural gas. [9] Fuel supply system according to any one of the preceding claims, characterized by that the fuel pump (2) has two or three pump elements (3).

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